The lead section (the opening paragraph) contains a “definition” of EE by John Wells. The quote comes from a web document called www.phon.ucl.ac.uk/home/estuary/ee-faqs-jcw.htm While the statement that EE is "Standard English spoken with the accent of the southeast of England" might serve as a rough pointer to what is being talked about, it does not seem to me to be what you could call a definition.
[Note: I have now rewritten most of the "Features" section of the article referred to below, so most of my criticisms of that section no longer apply]
The main part of the EE article is called “Features”, and is one of those “laundry list” bits of writing that you get when lots of different people add in their three-pennyworth. Some claims are dubious, some almost certainly wrong, and far too many are based on a single source (Joanna Przedlacka’s 2001 study, worthy though that is).
[I have now removed the material referred to below]
I will quote one case that strikes me as egregious. The “Features” section quotes Ken Lodge’s 2009 book A Critical Introduction to Phonetics as stating that “Estuary /əʊ/ may be pronounced [ɑːɪ̯̈] or [ɑːʏ̯̈], with the first element somewhat lengthened and much more open than in RP and the second element being near-close central, with or without lip rounding.” In addition, a vowel diagram purporting to be from Lodge’s book (p. 175) is reproduced showing the direction of travel for this diphthong. This doesn’t correspond to the diagram in the Lodge reference, and I wonder if the quotation is from somewhere else. To begin with, Lodge is not talking about (and doesn’t mention) Estuary English - he is, rather, talking about possible Australian influence on British English vowels. In his 2009 book, he says that the alternative vowel glide corresponding to RP /əʊ/ is [ɑəᵻ] or [ɑəʏ]; the diagram shows the former.
I won’t go into all the faults with the Features here. Some statements I find hard to believe, such as the claim that some Essex speakers have a clear [l] in ‘pull’. There is surprisingly little about glottalization of /p,t,k,tʃ/ and glottal replacement of /t/. To me the presence of intervocalic glottal stop for /t/ (e.g. ‘getting better’ as [ɡeʔɪŋ beʔə]) is one of the most salient characteristics of this accent, yet this article only mentions replacement of /t/ when it occurs pre-pausally and post-consonantally (the one example given is ‘can’t’ [kɑ:nʔ]).
The “Features” section contains two recorded examples, one of Ricky Gervais and one of Russell Brand. While these are good clear recordings, there is nothing in the text to indicate who has judged these two to be speakers of EE. Compare the article on RP, where the list of RP speakers has a citation to back up each claim.
To end the article, someone has added a section called Traditional Rural Estuary English which is about old Kentish and Essex accents. Looking at the history of recent edits this used to be very much longer but most of it has been moved to another article. What is left seems to me to shed little or no light on the present-day nature of EE and I think the article would be better if it was removed.